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  • 1
    Electronic Resource
    Electronic Resource
    The optical spectra of matrix-isolated palladium–nitrogen complexes: An investigation by absorption, emission, and photoelectron spectroscopy (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 1348-1354 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The optical spectra of palladium in neon and argon matrices containing up to 100% dinitrogen have been studied. Beside the known bands of isolated Pd atoms new strong bands assigned to weakly bonded Pd(N2)m (m=1, 2) complexes appear. The bands are attributed to three different types of transition. The dominant lines are essentially due to transitions localized at the Pd atom but strongly perturbed by a "crystal field'' due to the weakly bonded N2 molecules. Secondly, a vibrational progression at lower energies is assigned to a Pd to N2 charge transfer transition and thirdly, at high energies, a vibrational progression assigned to a locally excited state of an N2 molecule perturbed by weak bonding to Pd is observed. No evidence has been found for the presence of Pd(N2)3. Photoelectron spectra of the Pd(N2)m complexes in neon have been observed. The Pd 4d photoemission peak is shifted with respect to the Pd atom in Ne by ∼1.1 eV to higher binding energies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451222
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  • 2
    Electronic Resource
    Electronic Resource
    Optical spectra of matrix-isolated palladium atoms (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 6145-6149 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The optical properties of Pd atoms isolated in Ne, Ar, Kr, and Xe have been studied in the photon energy range of 2–10 eV by absorption, emission, and emission-yield spectroscopy. Strong matrix effects on the optical transitions are observed which lead to a breakdown of the selection rules and, hence, make a band assignment by AMCOR (atom to matrix correlation) impossible. The unusually large blue shift of the Pd 4d→5p transitions is rationalized by an interstitial site for the Pd atom in all four noble gas matrices. Such a site assignment is supported by the high mobility of the Pd atoms which becomes apparent in annealing experiments. For Pd in Ne, absorption bands due to 4d→4f transitions were found around 8 eV. Finally, a transient-absorption spectrum from a metastable state has been observed, which is in agreement with previously reported MCD measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449608
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  • 3
    Electronic Resource
    Electronic Resource
    The electronic spectra of matrix-isolated nickel atoms: The coexistence of the 3D3 and 3F4 ground states in Ar, Kr, and Xe (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 1623-1630 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic spectra of nickel atoms isolated in matrices of the four noble gases have been assigned in considerable detail. The associated experimental and theoretical study has unequivocally revealed that nickel atoms can simultaneously exist in two electronic ground states, 3d94s1:3D3 and 3d84s2:3F4, in argon, krypton, and xenon matrices where they also occupy at least three different trapping sites. In neon they appear to exist in one site and one state, 3d84s2:3F4, only. In argon, krypton, and xenon matrices the 3D3 is the dominant ground state. Some sites occupied by atoms in the 3F4 ground state can be annealed away, but others are found to be stable to this procedure. The effects of the matrix upon the guest atoms are briefly discussed. It is interesting that only one possible case of band splitting can be identified in the spectra though the observed blue shifts are of the usual magnitude.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448394
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  • 4
    Electronic Resource
    Electronic Resource
    Imaging of spatial pattern formation in an oscillatory surface reaction by scanning photoemission microscopy (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4942-4948 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rate of catalytic carbon monoxide oxidation on a Pt(100) single crystal surface under isothermal, low-pressure conditions exhibits for certain ranges of parameters (O2 and CO partial pressures, temperature) sustained temporal oscillations whose mechanism had been explored in previous work. Coupling between reaction and diffusion leads to spatial pattern formation as manifested by patches with different work function on the intrinsically homogeneous surface. Imaging is performed by means of the novel technique of scanning photoemission microscopy. Typically, nuclei with dimensions of a few microns, as determined by the instrumental resolution, are formed spontaneously and expand with sharp fronts and velocities of about 0.5 mm/min (at 480 K) up to sizes ≥1 mm. Waves with even more extended fronts propagating with somewhat higher velocities across the sample surface are responsible for the occurrence of large amplitude temporal oscillations of the integral reaction rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456735
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  • 5
    Electronic Resource
    Electronic Resource
    Reaction diffusion patterns in the catalytic CO-oxidation on Pt(110): Front propagation and spiral waves (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9977-9985 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamic behavior of elliptical front propagation and spiral-shaped excitation concentration waves associated with the catalytic oxidation of CO on a Pt(110)-surface was investigated by means of photoemission electron microscopy (PEEM). The properties of these patterns can be tuned through the control parameters, viz., the partial pressures of CO and O2 and the sample temperature. Over a wide range of control parameters the transition between two metastable states (COad and Oad covered surface) proceeds via nucleation and growth of elliptical reaction-diffusion (RD)-fronts. Front velocities and critical radii for nucleation are determined by the diffusion of adsorbed CO under reaction conditions. If at constant pO2, T the CO partial pressure is increased beyond a critical value a transition to qualitatively different dynamic behavior takes place. The elliptical fronts give way to oxygen spiral waves of excitation spreading across the CO-covered areas. For fixed experimental conditions a broad distribution of spatial wavelengths and temporal rotation periods was found. This effect has to be attributed to the existence of surface defects of μm-size to which the spiral tip is pinned. These data lead to a dispersion relation between the front propagation velocity and the wavelength, respectively, period. In addition, the dynamics of free spiral-shaped excitation waves was investigated under the influence of externally modulated temperature. Now the spiral starts to drift, resulting in distortion of the Archimedian shape and a pronounced Doppler effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464323
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  • 6
    Electronic Resource
    Electronic Resource
    Spatiotemporal concentration patterns associated with the catalytic oxidation of CO and Au covered Pt(110) surfaces (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8175-8184 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Submonolayers of gold were evaporated onto a Pt(110) surface in order to study the influence of surface modification on the formation of spatiotemporal concentration patterns during catalytic oxidation of carbon monoxide as imaged by means of photoemission electron microscopy (PEEM). Already the presence of 0.05 monolayers of uniformly distributed Au atoms affects markedly the kinetic parameters and thereby the properties of spatiotemporal patterns. The excitable regime is reached at lower CO pressures than with bare Pt(110), the width of the oxygen waves and the wavelength of spiral patterns decrease, the velocity of front propagation is reduced, and the density of nucleation centers for waves increases. The observed effects can be rationalized on the basis of the well-established underlying mechanism in terms of modification of the sticking coefficients for oxygen and carbon monoxide and of the diffusion coefficient for adsorbed CO. Additional effects such as penetration of waves into a monostable region, refraction, etc., come into play if waves pass the border between surface areas with differing chemical properties. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469229
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  • 7
    Electronic Resource
    Electronic Resource
    UV and VUV spectrum of matrix-isolated In: an investigation by absorption, magnetic circular dichroism and emission yield spectroscopy
    Amsterdam : Elsevier
    Chemical Physics 104 (1986), S. 435-448 
    Details
    ISSN: 0301-0104
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0301-0104(86)85033-9
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  • 8
    Electronic Resource
    Electronic Resource
    Coupling between adjacent crystal planes in heterogeneous catalysis by propagating reaction–diffusion waves (1994)
    [s.l.] : Nature Publishing Group
    Nature 370 (1994), S. 276-279 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The rate of a reaction catalysed by a uniform (that is, single-crystal) surface is usually formulated in terms of the surface concentrations (the partial coverages) of the reacting species and the associated rate constants. The associated set of coupled nonlinear differential equations generally ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/370276a0
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  • 9
    Electronic Resource
    Electronic Resource
    Imaging of spatio-temporal pattern evolution during carbon monoxide oxidation on platinum (1990)
    [s.l.] : Nature Publishing Group
    Nature 343 (1990), S. 355-357 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The catalytic formation of CO2 from CO and O2 on platinum proceeds by recombination of chemisorbed CO and O species, the latter originating from dissociative adsorption of O2. Under low-pressure conditions and for certain sets of control parameters (CO and O2 partial pressures, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/343355a0
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  • 10
    Electronic Resource
    Electronic Resource
    Imaging pattern formation: Bridging the pressure gap (1995)
    Springer
    Applied physics 61 (1995), S. 569-574 
    Details
    ISSN: 1432-0630
    Keywords: PACS: 82.65. Tv; 82.40.Ck
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract.  Two surface-sensitive optical imaging methods, Ellipso-Microscopy for Surface Imaging (EMSI) and Reflection Anisotropy Microscopy (RAM) are introduced. They allow imaging of pattern formation on surfaces, e.g., due to submonolayer coverages of adsorbates, at any arbitrary pressure. In spatio-temporal pattern formation during heterogeneously catalysed reactions this bridges the ‘pressure gap’ between well-defined UHV experiments and ‘real catalysis’. For the CO oxidation on Pt(110), the parameter space for pattern formation was extended up to 100 mbar, i.e., by 5 orders of magnitude compared to earlier investigations by Photo-Emission Electron Microscopy (PEEM) which had to be conducted below 10-3 mbar. With increasing pressure, the synchronisation mechanisms responsible for the observed pattern showed a gradual shift from reaction-diffusion to thermal-kinetic coupling unveiling previously unseen features of pattern formation in catalysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01542865
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